U.S. patent application number 15/031738 was filed with the patent office on 2016-12-22 for photocatalysts.
This patent application is currently assigned to Queen Mary University of London. The applicant listed for this patent is QUEEN MARY UNIVERSITY OF LONDON. Invention is credited to Steven Colin Dunn, Igor Larrosa Guerrero, Armando Marsden Lacerda Neto.
Application Number | 20160367968 15/031738 |
Document ID | / |
Family ID | 49767135 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160367968 |
Kind Code |
A1 |
Guerrero; Igor Larrosa ; et
al. |
December 22, 2016 |
Photocatalysts
Abstract
The present invention provides photocatalysts capable of
catalytic activity in the visible range of light comprising
platinum group metal nanoparticles deposited on a metal oxide
support. The nanoparticles have surface plasmon resonance in the
visible range of light. The invention also provides processes for
preparing the photocatalysts, methods of liquid and gas
purification using the photocatalysts of the invention and devices
for the same.
Inventors: |
Guerrero; Igor Larrosa;
(London, GB) ; Dunn; Steven Colin; (London,
GB) ; Neto; Armando Marsden Lacerda; (London,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUEEN MARY UNIVERSITY OF LONDON |
London |
|
GB |
|
|
Assignee: |
Queen Mary University of
London
London
GB
|
Family ID: |
49767135 |
Appl. No.: |
15/031738 |
Filed: |
October 24, 2014 |
PCT Filed: |
October 24, 2014 |
PCT NO: |
PCT/GB14/53191 |
371 Date: |
April 24, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 27/24 20130101;
A61L 2209/12 20130101; B01D 53/007 20130101; B01J 35/0013 20130101;
C01B 3/042 20130101; Y02W 10/37 20150501; C02F 2101/308 20130101;
A61L 9/18 20130101; B01J 21/063 20130101; B01J 23/42 20130101; B01J
35/002 20130101; Y02E 60/364 20130101; B01D 2259/802 20130101; B01J
23/44 20130101; C02F 2303/04 20130101; Y02E 60/36 20130101; B01J
37/06 20130101; C02F 1/30 20130101; C02F 2305/08 20130101; B01D
2255/802 20130101; B01J 35/004 20130101; C01B 13/0207 20130101;
C02F 2305/10 20130101; B01J 37/345 20130101 |
International
Class: |
B01J 23/44 20060101
B01J023/44; B01J 21/06 20060101 B01J021/06; B01J 37/34 20060101
B01J037/34; B01D 53/00 20060101 B01D053/00; C01B 3/04 20060101
C01B003/04; A61L 9/18 20060101 A61L009/18; C02F 1/30 20060101
C02F001/30; B01J 35/00 20060101 B01J035/00; B01J 37/06 20060101
B01J037/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2013 |
GB |
1318846.1 |
Claims
1. A photocatalyst capable of catalytic activity in the visible
range of light comprising amorphous platinum group metal
nanoparticles on a metal oxide.
2. A photocatalyst of claim 1, wherein the nanoparticles have
surface plasmon resonance in the visible range of light.
3. A photocatalyst according to claim 1 wherein the nanoparticles
are deposited on the metal oxide support, optionally by UV
photodeposition.
4. A photocatalyst according to claim 3 wherein the UV
photodeposition is carried out for less than 30 minutes.
5. A photocatalyst according to claim 1 wherein the nanoparticles
have a size of between about 2 and about 5 nm.
6. A photocatalyst according to claim 1 wherein the platinum group
metal is platinum or palladium.
7. A photocatalyst according to claim 1 wherein the metal oxide is
a refractory metal oxide.
8. A photocatalyst according to claim 7, wherein the refractory
metal oxide is titanium, chromium, zirconium, niobium, molybdenum,
hafnium or tungsten.
9. A photocatalyst according to claim 1, wherein the metal oxide is
a titanium metal oxide.
10. A photocatalyst according to claim 9, wherein the titanium
metal oxide is TiO.sub.2.
11. A photocatalyst according to claim 1 wherein the metal oxide is
doped.
12. A photocatalyst according to claim 11, wherein the
photocatalyst is doped with nitrogen.
13. A purification device comprising a photocatalyst according to
claim 1.
14. The purification device of claim 13, wherein the device
comprises a reaction chamber having an inlet and an outlet, and a
source of visible light, and further wherein the photocatalyst is
contained within the reaction chamber.
15. The purification device of claim 14, wherein the source of
visible light is external to the reaction chamber and the reaction
chamber is transparent to the visible light.
16. The purification device of claim 14, wherein the reaction
chamber inlet and reaction chamber outlet comprise valves for
controlling the flow of liquid or gas.
17. The purification device of claim 14, wherein the purification
device further comprises a storage chamber for storing purified
liquid or gas, wherein the storage chamber is in fluid
communication with the reaction chamber via the reaction chamber
outlet, optionally wherein the storage chamber further comprises a
dispensing outlet having a valve.
18. The purification device of claim 14, further comprising: a) a
pump for feeding liquid or gas into the reaction chamber via the
inlet; and/or b) a pump for expelling purified liquid or gas from
the reaction chamber via the outlet.
19. The purification device of claim 17 further comprising a pump
for dispensing purified liquid or gas from the storage chamber via
the dispensing outlet.
20. The purification device of claim 16, further comprising control
means for controlling the flow of liquid or gas through the
purification device, the control means being operably linked with
one or more of the valves and/or pumps.
21. The purification device of claim 14, further comprising means
for removing the photocatalyst from the purified liquid or gas.
22. A hydrogen production device comprising a photocatalyst
according to claim 1.
23. The hydrogen production device of claim 22, wherein the device
comprises a reaction chamber having a liquid inlet, a gas outlet,
and a source of visible light, and further wherein the
photocatalyst is contained within the reaction chamber.
24. The hydrogen production device of claim 23, further comprising
a storage chamber in fluid communication with the reaction chamber
for storing liberated hydrogen, optionally wherein the storage
chamber further comprises a dispensing outlet having a valve.
25. The hydrogen production device of claim 23, wherein the
reaction chamber further comprises a waste outlet.
26. The hydrogen production device of claim 23, further comprising
valves to control the flow liquid into the reaction chamber via the
liquid, the flow of gas out of the reaction chamber via the gas
outlet, and/or the flow of waste through the waste outlet.
27. The hydrogen production device of any claim 23, further
comprising: a) a pump for feeding liquid into the reaction chamber
via the liquid inlet; b) a pump for expelling liberated hydrogen
gas via the gas outlet; c) a pump for expelling waste via the waste
outlet, if present; and/or d) a pump for expelling purified gas
from the storage chamber via the dispensing outlet, if present.
28. The hydrogen production device of claim 23, further comprising
control means for controlling the flow of liquid or gas through the
hydrogen production device, the control means being operably linked
to one or more of the valves and/or pumps.
29. A process for preparing a photocatalyst capable of catalytic
activity in the visible range of light comprising depositing
platinum group metal nanoparticles on a metal oxide.
30. A process according to claim 29, wherein the platinum group
metal nanoparticles are deposited by irradiation.
31. A process according to claim 30 wherein the irradiation is
carried out by UV photodeposition and optionally the
photodeposition is carried out for less than 30 minutes.
32. A process according to claim 29 wherein the platinum group
metal is in solution.
33. A process according to claim 29 wherein the metal oxide is in
the form of solid, optionally a powder or in crystalline form.
34. A process according to claim 33 wherein the metal oxide solid
is added to a solution of the platinum group metal.
35. A process according to claim 29 wherein the photocatalyst is
dried after irradiation.
36. The process according to claim 29, wherein the metal oxide is
titanium dioxide.
37. A process according to claim 29, wherein the platinum group
metal is palladium.
38. A method of gas or liquid purification, sterilisation or
decontamination, comprising mixing the liquid or gas with a
photocatalyst of claim 1, and applying visible light to the
resulting mixture.
39. The method of claim 38, wherein the liquid is water.
40. The method of claim 38, wherein the gas is air.
41. A photocatalyst obtainable according to the process of claim
29.
Description
[0001] The present invention relates to novel photocatalysts and
uses thereof. The invention also relates to processes for preparing
the novel photocatalysts.
[0002] Fresh water is our planet's most valuable resource
accounting for less than 10% of all available water on the surface.
WHO estimates that 10% of the health burden can be relieved by
improving water quality. Poor water quality is especially a problem
in developing countries where studies suggest that up to 90% of
wastewater flows untreated into rivers, lakes and coastal zones. It
is estimated that polluted water affects the health of more than
1.2 billion people and contributes to the death of approximately 15
million children every year. Contamination of water by organic
compounds is a growing concern all over the world. Many organic
compounds can mimic hormones and have an effect on people at very
low concentrations. Others have been linked to different cancers.
Organic pollution also affects and can potentially destroy aquatic
ecosystems. Common sources of organic pollutants include industrial
effluents for example from chemical, textile and leather
industries, agricultural wastewater and domestic sewage.
[0003] Titanium dioxide (TiO.sub.2) is widely used as a
photocatalyst in water purification systems. It is a cheap,
naturally occurring, commonly available oxide of titanium and has a
good safety profile. A major drawback of TiO.sub.2 is that high
energy light such as ultraviolet (UV) light is necessary to
activate it, necessitating the use of an artificial, and usually
expensive, UV source in the purification system. UV light
constitutes approximately 2-4% of sunlight. The efficiency of
TiO.sub.2 is therefore limited by its ability to absorb only a
small fraction of the available light.
[0004] Papp et al. (Chem. Mater. 1993, 5, 284-288) disclose that
addition of palladium to TiO.sub.2 increases its photocatalytic
activity. However, UV light is still needed to activate the
TiO.sub.2.
[0005] There is therefore a need for a more efficient photocatalyst
that can show catalytic activity in the visible range of light.
[0006] The present invention provides novel photocatalysts having
improved photocatalytic activity in visible light.
[0007] The present invention provides photocatalysts capable of
catalytic activity in the visible range of light comprising
platinum group metal nanoparticles deposited on a metal oxide
support. The nanoparticles have surface plasmon resonance in the
visible range of light. The invention also provides processes for
preparing the photocatalysts, methods of liquid and gas
purification using the photocatalysts of the invention and devices
for the same.
[0008] In a first aspect of the invention there is provided a
photocatalyst comprising platinum group metal nanoparticles on a
metal oxide support. The nanoparticles have surface plasmon
resonance in the visible range of light. The photocatalysts are
capable of photocatalytic activity in the visible range of light.
The nanoparticles are deposited on the metal oxide and are
amorphous.
[0009] As used herein, "photocatalyst" refers to a substance that
increases the rate of a chemical reaction requiring the presence of
light. The catalytic activity of a photocatalyst depends on its
ability to generate electron-hole pairs which then participate in
and accelerate downstream reactions. As used herein, "visible range
of light" refers to the range of light visible to the naked human
eye. Generally, the visible range of light is electromagnetic
radiation with wavelength greater than or equal to about 380 nm,
390 nm, 400 nm, 410 nm, 420 nm, 430 nm, 440 nm or 450 nm, or up to
about 650 nm, 660 nm, 670 nm, 680 nm, 690 nm, 700 nm, 710 nm, 720
nm for example between about 390 nm and about 700 nm.
[0010] Platinum group metals include ruthenium, rhodium, palladium,
osmium, iridium, and platinum. In an embodiment of the invention
the platinum group metal is palladium or platinum. In some
embodiments, the platinum group metal is palladium.
[0011] Metal oxides (or other compounds for use in combination with
the platinum group metal) used in the invention include, but are
not limited to, titanium dioxide (TiO.sub.2), zinc oxide (ZnO),
cadmium sulfide (CdS), barium titanate (BaTiO.sub.3), zirconium
dioxide (ZrO2), tungsten oxide (WO.sub.3), potassium niobate
crystal (KNbO.sub.3), or strontium titanate (SrTO.sub.3).
[0012] In an embodiment of the invention the metal oxide is a
refractory metal oxide. Refractory metals include titanium,
chromium, zirconium, niobium, molybdenum, hafnium and tungsten.
[0013] In a preferred embodiment of the invention the metal oxide
is a titanium oxide, such as titanium dioxide (TiO.sub.2).
[0014] TiO.sub.2 has three main crystalline structures: anatase,
rutile and brookite. Degussa P-25 is a standard material in the
field of photocatalytic reactions containing anatase and rutile
phases in a ratio of about 3:1. The photocatalysts of the invention
comprising TiO.sub.2 may include anatase, rutile or brookite
crystalline structures, or a combination thereof. For example, the
photocatalysts of the invention comprising TiO.sub.2 may include a
combination of anatase and rutile phases, for example in a ratio of
about 3:1. In some embodiments, the photocatalysts do not contain
the brookite phase of TiO.sub.2.
[0015] In one embodiment the TiO.sub.2 (or other metal oxide) is in
a powdered form with an average particle size between about 20 and
about 25 nm, such as Degussa P-25 (CAS No. 13463-67-7, commercially
available from Evonik). The TiO.sub.2 (or other metal oxide), when
in powdered form, may have a surface specific area (BET) of between
about 30 and about 70 m.sup.2/g, for example between about 35 and
about 65 m.sup.2/g. The tapped density (according to DIN EN ISO
789/11, August 1983) may be about 100 to about 150 g/L, for example
between about 120 and about 140 g/L. The TiO.sub.2 (or other metal
oxide) may have a combination of these features, for example an
average particle size of between about 20 and about 25 nm, a
surface specific area of about 35 to about 65 m.sup.2/g, and
optionally a tapped density of between about 120 and about 140 g/L.
The photocatalyst may maintain some or all of these properties when
formed from such metal oxides.
[0016] Generally, the metal oxides are in a powder form (such as a
crystalline form), for example with an average particle diameter of
up to about 50 nm, optionally up to about 40 nm or up to about 30
nm. In some embodiments, the average particle diameter is more than
about 10 nm, for example more than about 20 nm. The average
particle diameter may be between about 10 and about 50 nm, for
example, between about 20 and about 30 nm, between about 20 and
about 25 nm and most preferably about 25 nm. Alternatively, the
metal oxides may be in solution, such as an aqueous solution, for
example between 1 and 10 g/L, or between 1 and 5 g/L, optionally 2
g/L. The solutions may be made using the powdered metal oxides
above. Similarly, the photocatalysts of the invention may be
present in a powdered (such as crystalline) form or in solution,
such as in water, optionally deionised water, or in suspension. The
physical properties of the photocatalysts may be as provided above
for the metal oxides.
[0017] As used herein, "nanoparticle" refers to any particle having
a diameter of less than about 1000 nanometers (nm).
[0018] In an embodiment of the invention the nanoparticles are
deposited on a metal oxide, in particular on the surface of the
metal oxide. The platinum metal can be considered a
co-catalyst.
[0019] In another embodiment of the invention the platinum group
metal nanoparticles are deposited on a metal oxide support. In some
embodiments, the nanoparticles are amorphous. In particular
embodiments, the nanoparticles are not in a crystalline form.
Generally, the atomic percentage of photo-deposited metal to metal
catalyst is about 0.4%, for example between about 0.3 and about
0.5%. In some embodiments, the atomic percentage of photo-deposited
metal to metal catalyst is up to 1%, optionally up to 7%, up to 5%
or up to 4%. In the case of a palladium-supported TiO.sub.2
photocatalyst, there may be an average of about 4 mg per gram of
palladium to titanium dioxide or about 5 mg per gram of palladium
to titanium dioxide. In some embodiments, there is up to about 10
mg of platinum group metal per gram of metal oxide, for example, up
to about 9 mg, up to about 8 mg, up to about 6 mg, up to about 5 mg
or up to about 4 mg platinum group metal to gram of metal oxide. In
some embodiments there is at least about 2 mg, about 3 mg, about 4
mg, about 5 mg or about 6 mg platinum group metal per gram of metal
oxide. In some embodiments, there is about 3 to 7, about 4 to about
6 or about 5 mg of platinum group metal per g of metal oxide in the
photocatalysts of the invention. In one embodiment of the
invention, there is about 4.8 to about 6.3 mg of platinum group
metal (such as palladium) per gram of metal oxide (such as
TiO.sub.2).
[0020] The metal oxide can also be doped to make it a better
catalyst. Doping is known in the art and refers to the process of
intentionally introducing impurities into a substance to enhance
the substance's charge carrier density. Doping of the metal oxide
generally occurs during the manufacture of the metal oxide prior to
the manufacture of the photocatalyst. Doping may be achieved using,
for example, nitrogen as the impurity. Other impurities may be
incorporated, for example platinum or noble group metals may be
used as dopants. Dopants are generally incorporated during the
synthesis procedure of the metal oxide (for example a titanium
metal oxide such as TiO.sub.2). The dopant ions usually replace an
ion in the metal oxide lattice, and so form part of the metal oxide
support that later has the nanoparticles deposited onto it. This
can be done using, for example, a hydrothermal synthesis procedure
of the catalyst. The amount of dopant present will depend on the
concentration of the dopant solution and other parameters of the
synthesis such as temperature and time.
[0021] In some embodiments, therefore, the photocatalyst of the
invention may further comprise an impurity, specifically a
deliberate impurity (dopant). In other embodiments of the
invention, however, the metal oxide is not doped.
[0022] The catalytic activity of TiO.sub.2 in the presence of light
has been studied intensively and is widely used for example in
water purification, hydrogen production and, antifogging coatings.
TiO.sub.2 can be used in water purification. Photocatalysts of the
present invention can be used in such applications as well.
[0023] The energy gap between the valence and conduction bands in
TiO.sub.2 is approximately 3-3.2eV. Due to this large band gap,
activation of TiO.sub.2 is usually restricted to high energy light,
i.e. ultra violet light (UV). In order to use visible light to
activate TiO.sub.2, this band gap needs to be reduced.
[0024] Upon activation by light, valence band electrons in
TiO.sub.2 are excited to the conduction band resulting in the
formation of electron-hole pairs which diffuse to the surface of
the TiO.sub.2. The electron in the conduction band participates in
reduction reactions whereas the hole in the valence band takes part
in oxidation reactions, each leading to the production of reactive
species. For example, when placed in water, the electron combines
with the oxygen in the water to form a reactive oxygen species such
as a superoxide anion or a peroxide and the hole leads to the
splitting of water into a hydroxyl radical and a proton. The
reactive oxygen species and hydroxyl radical are highly reactive
and interact with organic compounds in the water thus degrading
them.
[0025] The reactive species can also interact with the cell
membranes of microorganisms leading to lysis of the
microorganism.
[0026] In some embodiments of the invention the photocatalyst is
antimicrobial. There is therefore provided the use of the
photocatalysts of the invention as antimicrobial agents. There is
also provided a method of sterilising, purifying or decontaminating
a liquid or gas, comprising mixing a liquid or gas with a
photocatalyst of the invention and applying visible light to the
resulting mixture. The light activates the photocatalyst and the
liquid or gas is sterilised. The photocatalyst may be added to the
liquid or gas as a solid (for example a powder) or as a liquid (for
example in aqueous solution). In methods of the invention (methods
of sterilisation, purification or decontamination), the
photocatalyst may optionally be removed after
sterilisation/purification/decontamination.
[0027] Surface plasmon resonance (SPR) refers to the collective
resonance or oscillation of free electrons at the interface of a
solid or liquid and a dielectric in response to excitation by
incident light when the frequency of the incident light matches the
natural frequency of the electrons. A plasmon is a quantum of
collective oscillation of free electrons. It also refers to an
electromagnetic wave formed as a result of the collective
oscillation.
[0028] Palladium particles show plasmons in the UV range. However,
the inventors have found that palladium nanoparticles with particle
size between, for example, about 2 nm to about 5 nm show plasmons
in the visible range.
[0029] In a preferred embodiment of the invention, the platinum
group metal nanoparticle is a palladium nanoparticle.
[0030] In an embodiment of the invention the platinum group metal
(such as palladium) nanoparticle has a size (diameter) up to about
lOnm, about 8 nm, about 6 nm or preferably up to about 5 nm. In an
embodiment of the invention the platinum group metal (such as
palladium) nanoparticle has a size of at least about lnm, about 2
nm, about 3 nm or up to about 4 nm. In a preferred embodiment of
the invention the nanoparticles have an average size (diameter)
between about lnm and about 10 nm, about lnm and about 8 nm, about
2 nm and about 8 nm, about 2 nm and about 7 nm, about 2 nm and
about 6 nm, or about 2 nm and about 5 nm.
[0031] Nanoparticles can be deposited onto the metal oxide (such as
TiO.sub.2) via a photocatalytic mechanism or from nanoparticle
formation in solution followed by adsorption onto the surface. In
some embodiments of the invention the nanoparticles are deposited
by UV photodeposition.
[0032] UV photodeposition can be carried out for up to about 30
minutes, for example about 25 min, about 20 min, about 15 min,
about 10 min, about 5 min, about 1 min, about 30 seconds, about 15
seconds, about 10 seconds, about 5 seconds or about 1 second.
Generally speaking, a platinum group metal salt solution, for
example at a concentration of up to 0.02 mol/L, is mixed with the
metal oxide (for example up to 1 gram of the metal oxide such as
TiO.sub.2 (P25)). Optionally this can be done a glass dish fitted
with a quartz lid. The solution may be stirred under UV
irradiation. The resulting photocatalysts may be extracted from the
solution, for example by drying.
[0033] Rhodamine B is an organic compound that is commonly used as
a dye. The photocatalysts of the invention can be tested for
photocatalytic activity by measuring dye (such as Rhodamine B)
degradation. The photocatalysts of the invention can be tested for
catalytic activity by measuring the degradations of other compounds
such as chlorobenzene compounds, sodium dodecylbenzenesulphonate
(DBS) or benzoic acids. Dyes other than Rhodamine B include methyl
orange and methylene blue. Degradation of dyes can be measured by
decolourisation (for example using a colorimeter). Degradation of
other compounds can be measured by, for example, gas
chromatography. Alternatively, the total organic content (total
amount of carbon at the beginning and at different points during
the reaction process over time) can be measured. A standard
reaction for measuring the photocatalytic activity of a test
compound (such as TiO.sub.2) is typically the measurement of the
decrease in concentration of a pollutant introduced to an aqueous
solution in the presence of an irradiation source to activate the
catalyst. The pollutant may be a compound that degrades on
activation of the photocatalyst, such as a dye (for example
Rhodamine B, methyl orange and methylene blue), or other compound
such as chlorobenzene compounds, sodium dodecylbenzenesulphonate
(DBS) or benzoic acids.
[0034] Generally, the photocatalysts of the invention will catalyse
a reaction (for example the degradation of Rhodamine B) by up to
about 5-fold, for example up to about 10-fold, up to about 15-fold,
up to about 20-fold, up to about 25-fold or up to about 30-fold.
The photocatalysts of the invention may catalyse such a reaction by
at least about 10-fold or by at least about 15-fold or by at least
about 20-fold or by at least about 25-fold. In some embodiments,
the photocatalysts catalyse reactions, such as the degradation of
Rhodamine B, by between about 5 and about 30-fold, for example
between about 10 and about 30-fold or between about 15 and about
30-fold.
[0035] In a second aspect of the invention there is provided a
purification device comprising a photocatalyst according to the
first aspect of the invention. The device may be a liquid (eg
water) or gas (eg air) purification device. Sterilisation and
decontamination devices are also provided, and these have the same
features as the described purification devices.
[0036] A purification device as provided herein generally refers to
a liquid purification system or a gas purification system. In an
embodiment of the invention, the liquid purification system is a
water purification system.
[0037] TiO.sub.2 is very commonly used in water purification
systems. A water purification system typically comprises a polluted
water inlet, a purification chamber and a treated water outlet. The
purification chamber of the prior art comprises TiO.sub.2 and a UV
light source. Polluted water enters the system through the inlet
and interacts with the TiO.sub.2, which is activated by the UV
light resulting in the formation of reactive species. Organic
compounds and microorganisms in the water are degraded by the
reactive species and the purified water exits the system through
the outlet. The purification chamber may also act as a storage
chamber, or alternatively there may be a storage chamber in fluid
communication with the purification chamber via the water outlet
where purified water is stored until it is required. The storage
chamber may itself have a further water outlet allowing the
purified water to be dispensed from the purification device.
[0038] The TiO.sub.2 in a water purification system, such as of the
type described above, can be replaced with the photocatalyst of the
invention and hence in embodiments of the invention the water
purification system includes a photocatalyst of the invention in
the purification chamber. Thus visible light can be used to
activate the catalyst and purify the water. However, UV light can
still be used since the catalysts of the invention are capable of
catalysis in the UV spectrum (for example between 10 and 400 nm or
between 10 and 390 nm) as well as in the visible light
spectrum.
[0039] In an embodiment of the invention the gas purification
system is an air purification system.
[0040] The purification devices of the invention comprise a
reaction chamber having an inlet and an outlet. The reaction
chamber comprises the photocatalyst of the invention and this is
where the purification takes place. Up to about lg, up to about
500mg, up to about 100 mg or up to about 50mg of photocatalyst may
be present. In some embodiments, at least about 10mg, at least
about 50mg, at least about 100mg or at least about 500mg of
photocatalyst may be present. In the case of liquid purification
systems, the photocatalyst may be present in solution or
suspension. In the case of gas purification systems, the
photocatalyst may be present as a bed of solid or powdered catalyst
through or over which the gas to be purified flows.
[0041] The inlet is an inlet for the liquid or gas to be purified.
In some embodiments, for example in the case of a liquid
purification device, the inlet may simply be a removable lid of the
reaction chamber, although in other embodiments the inlet may be a
hollow conduit (such as a pipe). The outlet is for purified liquid
or gas, and similarly may be a hollow conduit (such as a pipe). The
inlet may comprise a filter for removing particulate contaminants.
The outlet pipe may comprise means for removing the photocatalyst
from the purified liquid or gas, such as a filter.
[0042] Alternatively, the means for removing the catalyst may be a
centrifuge or a means for distillation that is in fluid
communication with the reaction chamber via the reaction chamber
outlet.
[0043] The purification device may optionally include a source of
light, such as a source of visible light. The reaction chamber may
be transparent, for example if the source of light located
externally to the reaction chamber. Alternatively, the source of
light may be located inside the reaction chamber. The source of
light may be operably linked to a control means that allows a user
to activate or deactivate the source of light.
[0044] The purification device may further comprise a storage
chamber to store purified liquid or gas. The storage chamber, if
present, is in fluid communication with the reaction chamber via
the reaction chamber outlet. The storage chamber may further
comprise a dispensing outlet having a valve.
[0045] The storage chamber may itself be connected to a means for
removing the photocatalyst described herein, for example via its
dispensing outlet. Alternatively, the means for removing the
photocatalyst described herein may comprise a chamber in fluid
communication with the reaction chamber via the reaction chamber
outlet. The chamber of the means for removing the photocatalyst may
then be in further fluid communication with the storage chamber via
a storage chamber inlet. The storage chamber is therefore useful
for storing purified liquid or gas from which the photocatalyst has
been removed.
[0046] Pumps may also be present. For example, there may be a pump
for feeding gas or liquid into the reaction chamber via the inlet
and/or a pump for expelling purified gas or liquid from the
reaction chamber via the outlet (optionally into the storage
chamber, if present). If a storage chamber with dispensing outlet
is present, the flow of liquid or gas through the dispending outlet
may be effected by means of a pump (optionally operably linked to a
control means).
[0047] Generally, the inlets and outlets will comprise valves for
controlling the flow of water through them. Control means may be
present that are operably linked to the valves so a user can
control the flow of liquid or gas. In particular, the purification
device may comprise a control means that is operably linked to the
valve of the reaction chamber outlet (or the valve of the storage
chamber dispensing outlet) allowing purified liquid or gas to be
dispensed. The control means may also be operably linked to any
pumps present.
[0048] The purification device may include a storage chamber and
further a feedback loop for recirculating the liquid or gas
multiple times. The feedback loop allows the liquid or gas to exit
and then re-enter the reaction chamber. In such embodiments, the
feedback loop comprises a valve that determines the flow of the
liquid or gas either through the reaction chamber outlet into the
storage chamber (once the liquid or gas is suitably purified) or
back into the reaction chamber via a conduit to permit further
purification. The purification device may include means for testing
the level of purification of the gas or liquid. This allows a user
to determine when a suitable amount of purification has taken
place, or this may be done automatically by the system itself.
Optionally, the means for testing the level of purification in the
liquid or gas is located in the feedback loop and is operably
linked to the valve therein, such that the system automatically
recirculates polluted liquid or gas until a desired level of
purification has taken place.
[0049] In a third aspect of the invention there is provided a
hydrogen production device.
[0050] The apparatus for the production of hydrogen from water or
aqueous solutions of organic compounds by using the catalyst
comprises a light source (such as a visible light source), a
reactor (optionally wherein the reactor is transparent for the
light of the light source if the light source is external to the
reactor), an inlet for feeding water or aqueous solution to the
reactor, and a gas product outlet for releasing hydrogen liberated
in the reaction chamber. The photocatalyst of the invention is
present in the reactor. The apparatus for the production of
hydrogen may further comprise a storage chamber for collecting and
storing the hydrogen produced. The storage chamber is in
communication with the reaction chamber via the gas outlet. The
storage chamber may be pressurised.
[0051] Valves may also be present, to control the flow of water or
aqueous solution into the reactor via the inlet and release of gas
via the outlet. Control means also be present to adjust the light
source intensity or even switch it on or off as required. The
reaction chamber may further comprises a waste outlet for removal
of waste or by-products or unreacted water or aqueous solution, the
waste outlet optionally having a valve. Still further, the hydrogen
production device may comprise control means operably linked to the
valves for controlling the flow water or aqueous solution into the
reaction chamber, the flow of hydrogen through the outlet (and into
the storage chamber if present), and/or the flow of waste or
by-products or unreacted water or aqueous solution through the
waste outlet.
[0052] In devices of the invention (purification, decontamination,
sterilisation or hydrogen production devices), the photocatalyst of
the invention may be present in the reaction chamber as a solid (eg
a powder or in crystalline form), or alternatively it may be
present in solution, such as in an aqueous solution, or suspension.
The devices may further comprise a means for adding the
photocatalyst to the reaction chamber (or for replenishing the
photocatalyst), for example a photocatalyst inlet in communication
with the reaction chamber. The means for adding the photocatalyst
to the reaction chamber may be a removable lid of the reaction
chamber. Such a lid would also facilitate cleaning and
maintenance.
[0053] In a fourth aspect of the invention there is provided a
process for preparing a photocatalyst of the invention. The process
comprises depositing a platinum group metal (such as palladium) on
a metal oxide (for example an oxide of a refractory metal, such as
a titanium oxide). The platinum group metal is deposited in the
form of nanoparticles. The nanoparticles have a surface plasmon
resonance in the visible range of light. Generally, a powdered or
crystalline form of the metal oxide is added to a solution of the
platinum group metal (such as an aqueous solution). The solution of
platinum group metal may be acidified (for example using
hydrochloric acid or other acid) to increase the solubility of the
platinum metal. Generally, the platinum metal is present in the
form of a salt, for example a chloride salt (such as palladium
chloride, which can be prepared by dissolving palladium chloride
powder in hydrochloric acid, followed by sonication and/or stirring
in a water bath). Light is then used to irradiate the solution
containing the metal oxide and the platinum group metal. Generally
this is achieved with UV light. It is thought that the UV light
changes the valence of the platinum metal to zero (for example,
palladium 2 to palladium 0) such that the platinum metal is then
deposited on the metal oxide. The platinum metal is deposited on
the metal oxide in the form of amorphous nanoparticles.
[0054] In some embodiments, photodeposition (for example UV
photodeposition) of the platinum group metal by irradiation is
carried out for less than about 60 minutes, less than about 50
minutes, less than about 40 minutes, less than about 30 minutes,
less than about 20 minutes or less than about 10 minutes. In some
embodiments the photodeposition is carried out for less than about
30 minutes.
[0055] Alternatively, the platinum group metal can be deposited
onto the metal oxide via a photocatalytic mechanism or from
nanoparticle formation in solution followed by adsorption onto the
surface of the metal oxide. Preferably, the nanoparticles are
deposited in an amorphous form on the metal oxide. Optionally, the
method comprises the further steps of washing and/or drying the
photocatalyst. The process for the preparation of the
photocatalysts of the invention may further comprise a step of
doping the photocatalyst. The metal oxide may be doped prior to or
after mixing with the platinum group metal solution, although
generally before mixing with the platinum group metal solution. In
particular, the metal oxide may be doped by introducing deliberate
impurities during the production of the metal oxide, such that the
method of photocatalyst production is carried out on a pre-doped
metal oxide.
[0056] There is also provided a photocatalyst of the invention
preparable by the process described herein.
[0057] In a fifth aspect of the invention there is provided a
method of purifying (or sterilising or decontaminating) a liquid or
gas comprising adding a photocatalyst of the liquid or gas and
exposing the liquid or gas to light in the visible range. The
liquid may be water, or the gas may be air. The liquid or gas may
be exposed to the light for as long as is required to purify the
liquid or gas to a satisfactory degree. For example, the water may
be exposed to the light for at least about 1 minute, at least about
5 minutes, at least about 10 minutes, at least about 30 minutes, at
least about 60 minutes or at least about 120 minutes. The liquid
may be purified to the extent that the amount of contaminants is
reduced by at least about 20%, at least about 30%, at least about
40%, at least about 50%, at least about 60%, at least about 70%, at
least about 80%, at least about 90%, at least about 95%, at least
about 98%, at least about 99% or about 100%. The contaminants that
are removed may include organic molecules and/or dyes. The
purification, sterilisation or decontamination process may take
place in a purification, sterilisation or decontamination device of
the invention.
[0058] Generally, the photocatalyst of the invention will be
removed following purification. This removal can be achieved using,
for example, centrifugation or distillation.
[0059] Methods of liquid or gas purification may further comprise
the steps of determining the level of liquid or gas purification,
and repeating the purification steps if the liquid or gas has not
reached the desired level of purity.
[0060] In a sixth aspect of the invention there is provided a
method of purifying a gas (for example air) by passing the gas over
or through a photocatalyst of the invention. The gas may be passed
over or through the photocatalyst such that the level of impurities
in the gas is reduced by desired amount. A gas being purified may
be recirculated such that it is exposed to the photocatalyst of the
invention multiple times. The gas may be passed through a bed of
the photocatalyst. Alternatively, the gas may be mixed with the
photocatalyst in solution (such as aqueous solution), for example
the gas may be bubbled through a solution of the photocatalyst.
[0061] The method of gas purification may further comprises the
steps of determining the level of gas purification, and repeating
the purification steps if the gas has not reached the desired level
of purity.
[0062] There is also provided the use of a photocatalyst of the
invention in the purification of a liquid (such as water) or a gas
(such as air). There is further provided the use of a photocatalyst
of the invention as a gas or liquid purifier or steriliser. There
is also provided the use of a photocatalyst in a method of liquid
or gas decontamination.
[0063] In one embodiment of the invention there is provided a
photocatalyst comprising palladium amorphous nanoparticles
deposited on a TiO.sub.2 support. The nanoparticles have a surface
plasmon resonance in the visible range of light. Thus the
photocatalyst is capable of catalytic activity in the visible range
of light (for example, between 390 to 700 nm). The photocatalysts
can be used to purify water by catalysing the degradation of
contaminants and/or disrupting cell membranes of microorganisms
leading to lysis of the microorganism.
[0064] Preferred features of the second and subsequent aspects of
the invention are as provided for the first aspect, mutatis
mutandis.
[0065] The invention will now be further described by way of
reference to the following Examples which are present for the
purposes of reference only and are not to be construed as being
limiting on the invention. In the Examples, reference is made to a
number of drawings in which:
[0066] FIG. 1 shows the spectral output of a Honle UVACUBE.
[0067] FIG. 2 shows the decolourisation of Rhodamine B by the
Pd--TiO2 photocatalyst under solar conditions.
[0068] FIG. 3 shows the irradiation spectrum of the solar simulator
with different filters.
[0069] FIG. 4 shows the decolourisation rates of the catalyst under
different filters compared with TiO.sub.2 under solar
conditions.
[0070] FIG. 5 shows the half-life of dye degradation versus plasmon
peak position and the modelled plasmon absorption.
[0071] FIG. 6 shows the cut-off points for the different filters
used (6a) and the decolourisation rates of the catalyst using
different filters
[0072] FIG. 7 shows the TEM micrograph of the Pd deposited on
TiO.sub.2.
EXAMPLES
Example 1
Photocatalysts Synthesis Procedure
[0073] Different photocatalysts were prepared using the following
protocol as shown in Table 1.
TABLE-US-00001 TABLE 1 irradiation Plasmon Pd per gram of dye
t.sub.1/2/ time/ peak/ Catalyst catalyst/mg adsorption/% min min nm
10 ml 0.01M PdCl.sub.2 @ 2.05 mW/cm.sup.2 AL094 5.331 18.3 0.53 1
446 10 ml 0.01M PdCl.sub.2 @ 9.54 mW/cm.sup.2 AL096 5.451 20.5 0.63
1 442 AL097 4.851 10.1 0.43 0.167 438 5 ml 0.02M PdCl.sub.2 @ 9.54
mW/cm.sup.2 AL098 5.817 11.4 0.66 30 453 AL099 5.924 18.6 0.55 3
438 5 ml 0.02M PdCl.sub.2 @ 2.05 mW/cm.sup.2 AL103 5.886 15.1 0.58
3 448 10 ml 0.02M PdCl.sub.2 @ 9.54 mW/cm.sup.2 AL106 6.118 14.2
0.46 30 454 AL108 5.845 12.3 0.38 0.167 439 10 ml 0.02M PdCl.sub.2
@ 2.05 mW/cm.sup.2 AL109 6.272 13.9 0.36 30 454 AL114 6.46 10.9
0.46 3 447 AL110 5.407 14.6 0.52 1 428 AL111 6.281 22.2 0.53 0.167
425
[0074] Stock Solution Preparation
[0075] The palladium chloride (PdCl.sub.2) stock solution from
which the Pd metal is reduced onto the titanium dioxide (TiO.sub.2)
is prepared by dissolving 177.326mg of PdCl.sub.2 powder (for a
0.01 M solution) in 100 ml of 0.01M hydrogen chloride (HCl). First
the powder and solution mixture is sonicated in a sonic bath for 30
minutes then stirred with a magnetic stir bar until the PdCl.sub.2
is completely dissolved.
[0076] Photoreduction Procedure
[0077] For each catalyst synthesis the type of TiO.sub.2 used is
Degussa P25 nanopowder with an average particle size of 25 nm. The
amount used per reaction is fixed at 1 gram.
[0078] The reaction vessel consists of a 50 mm diameter (10 mm
deep) glass Petri dish containing a magnetic stir bar and sealed
with a 50 mm.times.50 mm x lmm quartz lid to minimise evaporation
during the procedure. 10 ml of PdCl.sub.2 solution at either 0.01 M
or 0.02M is used and mixed with the TiO2 for 1 minute prior to
irradiation. The slurry is continuously stirred throughout
irradiation during each photoreduction.
[0079] The irradiation source used is a Honle UVACUBE with a
spectral output as shown in FIG. 1. Two irradiance values are used
for the synthesis and these are altered by changing the distance
between the irradiation source and the top of the solution inside
the reaction vessel. The minimum value is 2.05 mWcm-2 and the
maximum is 9.54 mWcm-2. Irradiation times are 30 minutes, 3
minutes, 1 minute, 10 seconds and 1 second.
[0080] Washing Procedure
[0081] After irradiation the slurry is transferred to a glass vial
using a pipette and stored in the dark for 24 hours to allow the
powder to settle. After this time the powder and solution are
separated by pipette and the powder is allowed to air dry at room
temperature. Once the powder is dry it is transferred to a filter
system thoroughly washed with deionised water, up to 250 ml, on a
paper filter base that allows the water to run through. The
catalyst is then left to air dry again. When the powder is dry it
is loosened with a pestle and mortar and stored in a sealed glass
vial.
Example 2
Rhodamine B Degradation
[0082] The decolourisation of Rhodamine B (RhB) was carried out
using a 50 ml solution at a concentration of 10 ppm (FIG. 2). 100
mg of the Pd--TiO2 catalyst was added to the solution and the
mixture was stirred in the dark using a magnetic stir bar for 30
minutes to allow for adsorption-desorption equilibrium. The mixture
was then irradiated under simulated solar condition at AM 1.5 and
aliquots were taken at predetermined time intervals and centrifuged
at 4000 rpm for 30 minutes to separate catalyst from solution. The
solutions were then subjected to UV-vis analysis to determine the
decolourisation rate. The rate of decolourisation was determined
from the Langmuir-Hinshelwood model:
r = - C A t ##EQU00001##
[0083] where r is the rate of decolourisation, CA, is the
concentration of solution and t is the time of irradiation.
[0084] An experiment was carried out to test the catalyst under
more specific regions of the EM spectrum by using optical cut-off
filters. Filters used were a UV light blocking filter (UV-block), a
visible light blocking filter (vis-block) and a visible light pass
filter (vis-pass). The Pd--TiO2 catalyst was used to decolourise
RhB dye in 4 separate experiments under different irradiation
conditions for each. The results of the experiments were compared
with the decolourisation of TiO.sub.2 under solar conditions
without any filters. FIG. 3 shows the irradiation spectrum of the
solar simulator with each of the filters attached. FIG. 4 shows the
results of the 4 experiments. Decolourisation of dye by the
Pd--TiO.sub.2 without filter showed the most activity of any of the
other experiments. The UV-block and vis-pass filters yielded
similar results and were the least active of the experiments, which
were comparable to the rate of decolourisation of dye in the
presence of just TiO.sub.2 under solar conditions without filter.
The vis-block filter yielded an intermediate rate. Since TiO.sub.2
is deactivated in the absence of UV, this suggests that it is the
plasmon that is responsible for the absorption in the visible
range. From the plasmon modelling data, it is clear that the centre
of the plasmon sits at a region where the broad peak extends into
the UV, as well as the visible region. This is further confirmed by
the vis-block experimental data where the decolourisation rate
increases, which can be attributed to the activation of both the
TiO.sub.2 absorption and plasmon absorption, but the visible
portion of the plasmon absorption has been cut-off, leading to a
decrease in activity relative to the no-block data.
Example 3
Surface Plasmon Analysis
[0085] The data presented here have been collected from experiments
designed to test the activity of the catalyst by determining the
half-life of decolourisation of Rhodamine B and also from
measurements of the plasmon absorption peak using a UV-vis
spectrophotometer. The raw data from the UV-vis analysis was used
to model the plasmon based on a Gaussian function and fitted to the
original data. The modelled plasmon and the measured plasmon
absorption were consistently in good agreement and the model was
used to obtain a value for the absorption of the resonance
peak.
[0086] FIG. 5 shows the half-life of dye degradation versus plasmon
peak position (a and b) and the modelled plasmon absorption (c and
d). The irradiance value is clearly stated in the graph titles.
[0087] Dye decolourisation experiments using optical band-pass
filters indicate that the increased absorption of the Pd--TiO.sub.2
catalyst is due to the presence of localised SPR. This is evident
when a UV cut-off filter was used to `deactivate` the TiO.sub.2 by
prohibiting the incidence of super band gap photons, (FIG. 3 and
FIG. 4), into the reaction vessel. Despite the presence of the
cut-off filter, a significant amount of RhB decolourisation under
visible light irradiation still occurred and is thought to be
attributed to the plasmon. By blocking visible light irradiation,
an even greater amount of dye was degraded in the same time frame
relative to UV-blocking. This suggests that the plasmon is also
active in the UV region, contributing to the overall degradation
under these conditions. This is supported by the modelled plasmon
peak showing a broad absorption extending into the UV from its
central point. FIG. 7 shows the absorption of TiO2 Degussa P25
before photochemical deposition of Pd metal compared with the
absorption of the Pd--TiO.sub.2 catalyst. The modelled plasmon and
the broadband irradiation spectrum used for photodegradation are
also included. The inset shows the results of photodecolourisation
of RhB of TiO.sub.2 compared with the Pd--TiO.sub.2 catalyst under
simulated solar conditions.
[0088] The structure and size of the Pd nanoparticles were
confirmed by TEM analysis. The micrographs reveal that the Pd
nanoparticles are amorphous in nature and have a diameter of less
than 5 nm as shown in FIG. 8.
* * * * *